A method for habitat assessment in agricultural landscapes

The need for a conservation policy for remnant semi-natural vegetation in the agricultural landscape of lowland Britain is stressed. An essential prerequisite for such a policy involves the formulation of a method for habitat assessment which may provide relevant ecological information to planners, land owners and land managers. Existing techniques of ecological evaluation and their problems are briefly reviewed and a new approach, habitat inventory analysis, is described. In addition to measures of habitat and species diversity, variables related to the size and fragmentation of remnant habitats are emphasized and the potential of selected techniques of multivariate analysis for ordering the data is demonstrated. Examples of the use of the method in parts of Cornwall and Dorset are presented and the complete methodology is critically discussed.     

Geology of the Atlantis Massif (Mid-Atlantic Ridge, 30° N): Implications for the evolution of an ultramafic oceanic core complex

Marine Geophysical Research - The oceanic core complex comprising Atlantis Massif was formed within the past 1.5–2 Myr at the intersection of the Mid-Atlantic Ridge, 30° N, and the...     

Patterns and drivers of asteroid abundances and assemblages on the continental margin of Atlantic Canada

Although continental shelf and slope environments typically exhibit high epifaunal biomass and have been subjected to increasing fishing pressure, ecological information on assemblages of non‐commercial invertebrate species from subtidal and bathyal areas remains limited. Sea stars (Echinodermata: Asteroidea), which are known to influence communities through their feeding habits, have received less attention than structural taxa such as corals and sponges. To better understand the ecological roles of asteroids on continental shelves, we investigated ~30 species and assessed their distributions and co‐occurrence with other benthic invertebrates on the shelf and slope of Eastern Canada. Using fisheries data and in situ video footage, we compiled a large dataset covering ~600,000 km² that included over 350,000 individual asteroid records (37–2243 m depth). Multivariate analyses revealed geographically distinct asteroid assemblages, with a maximal overall density at 400–500 m and the highest diversity at 500–700 m. The most abundant and densely occurring species was Ctenodiscus crispatus. We found that asteroids associate with corals, sponges, bivalves, and other echinoderms, and that depth and substrate influence these assemblages. We identified species likely to affect coexisting organisms by their burrowing behavior that can disrupt epi‐ and infauna (C. crispatus) and through predation on ecologically important corals (Hippasteria phrygiana). In addition to providing baseline distribution and ecological information for many bathyal asteroid species in the Northwest Atlantic, this work highlights the abundance and diversified roles of asteroids within continental shelf and slope ecosystems.     

Multiple-impact mechanisms on Venus and other solid planets and satellites

While atmospheric pressure can be considered a major multiple impact mechanism on Venus, probable mechanisms for multiple impacts on other solid planetary bodies cannot be isolated with certainty.     

ANOMALOUS WET AND DRY SPELLS IN THE CENTRAL UNITED STATES, 1931–75

The Palmer Index (PI) was employed to compare anomalous dry spells with anomalous wet spells for 76 climatic divisions in the central United States. Comparisons were made in terms of the frequency, severity and persistence of wet and dry climatic episodes for the period 1931–75. The results indicated more frequent dry anomalies in the southwest (New Mexico and west Texas) portion of the study area and more frequent wet anomalies in the northeast (Illinois and Iowa). Not surprisingly, these are the most arid and most humid portions respectively. The results of the analysis for persistence were less clear. Typically dry anomalies lasted longer than wet anomalies, especially as the minimum length was increased. This was especially apparent when comparing the very longest dry spell with the very longest wet spell during the 45-year study period. Thus there are more but shorter wet spells and less frequent, but typically longer lasting dry spells. This final relationship posits the question of feedback processes between surface soil moisture and the persistence of atmospheric precipitation anomalies. [Key Words: Palmer Index, drought, moisture anomalies, wet spells, dry spells.]     

Deep secrets of a sun and surf resort in the Atlantic

The majority of igneous rocks can be classified into either the basalt–gabbro group, or the rhyolite–granite group. However, there also exist a wide range of rocks whose composition lies outside these broad groupings, some of which are compositionally extreme and contain many rare minerals, sometimes as essential components. Petrologists have always interested themselves in these unusual rock types, just as collectors always value rare items over the commonplace. Many of these unusual rock types have been given weird and wonderful names, driving non‐petrologists to distraction, although a more scientific system of nomenclature has yet to receive general acclaim. The giving of a plethora of names to igneous rocks was largely a phenomenon of the early years of petrology in the late nineteenth and early twentieth century and many will be surprised to learn that new names are still being coined as with the, as yet unauthorized, bermudite, not surprisingly, called after the island of Bermuda.     

Rare earth element distributions in a proto-stratiform ultramafic intrusion

Rare earth element (REE) abundances are reported for ten whole rock and eight mineral samples from the Preacher Creek ultramafic intrusion of southeastern Wyoming. Chondrite-normalized distribution patterns for the whole rocks exhibit a broad maximum between Sm and Gd and reflect the REE pattern of clinopyroxene, the major REE-bearing phase. Alteration of the primary mineral assemblages to actinolite and chlorite, which is generally minor, does not appear to have significantly affected the REE distributions. Absolute abundances of the REE in the rocks and constituent minerals increase as a function of differentiation, and relative abundances suggest an accompanying light REE enrichment. Trapped-liquid phases, which may be relatively enriched in REE, possibly account for some or all of the observed REE trends. The REE data, interpreted in terms of crystal-melt fractionation, suggest derivation of the intrusion by crystallization from a gabbroic magma having a REE distribution pattern similar to the parent magma of the Skaergaard stratiform complex. The results of this study are in accord with and complement a previous proposal that the Preacher Creek body formed in a manner analogous to major stratiform intrusions.     

Messengers from the deep – the mantle under the North Atlantic area

Only the very outermost skin of the Earth will ever be directly accessible with the deepest boreholes extending to only about 10 km. This is negligible compared to the distance to the core of around 6000 km, or even the base of the crust, which is tens of kilometres thick under the continents. Nevertheless, we can gain information about the deep regions of the earth by two means: geophysics, and situations where deep rocks have become exposed at the surface.     

Water and nitrogen movement through a semiarid dryland agricultural catchment: Seasonal and decadal trends

Water and nutrient budgets in dryland agroecosystems are difficult to manage for efficiency and water quality. This is particularly true where complex terrain and soilscapes interact with pronounced hydrologic seasonality. The purpose of this research was to understand water and hydrologic nitrogen (N) export from a hillslope dryland agroecosystem in a semiarid region where most precipitation occurs outside the growing season. We studied 13 years (2001–2013) of records of water and N inputs and outputs from a 12 ha no‐till artificially drained catchment in the semiarid Palouse Basin of eastern Washington State, USA. Fall‐ and winter‐dominated annual precipitation averaged 462 mm. About 350 mm went to evapotranspiration; crops used ~160 mm from stored soil water during the summer dry‐down season. Soil water replenishment after crop senescence, during the fall wet‐up season, delayed the threshold onset of the high‐discharge season until December. Winter‐dominated drainage fluxes averaged 111 mm or 24% of annual precipitation. Nitrate export in drainage averaged 15 kg·N·ha^?1·year^?1, which was about 10 times the average rate of dissolved organic N export and 15% of the average rate of N application in chemical fertilizer. Fertilizer applications to the catchment were reduced, due to cropping changes, by 1/3 during the last 5 years of the study; however, no corresponding reduction was observed in the nitrate export flux. This lack of change could not be attributed to mineralization of the soil‐organic N legacy of fertilization nor to hydrologic lag of the catchment. Likeliest explanations are (a) despite the reduction, N application continued to exceed crop uptake and accumulation in organic matter; (b) seasonal and interannual variability of catchment connectivity resulted in year‐to‐year field‐scale nitrate storage and carryover. Water and N use efficiencies observed here may be near maximum obtainable for existing crops in this climate. Substantial improvements that would also address multiple environmental issues associated with the N cascade may involve shifts to perennial systems and/or rotations in which N is fixed biologically.     

Evolution of the skærgaard magma: evidence from crystallized melt inclusions

Polymineralic aggregates composed of clinopyroxene, Fe-Ti oxide minerals, apatite and accessory K-feldspar, biotite, and amphibole are enclosed in cumulus plagioclase grains in the Middle Zone of the Skærgaard intrusion. The chemistry of the minerals in the aggregates, and the textural relations between the aggregates and the host plagioclase grains indicate that they represent inclusions of the contemporaneous melt of the Skærgaard intrusion. Through mass balance calculations a quantitative estimate of the melt composition for this level in the intrusion can be obtained, and this estimate confirms that the silica content in the Middle Zone melt was similar to, or possibly even lower than, the silica content in the initial Skærgaard melt, and relatively enriched in iron.